AERATION
Supplying soil and roots with air or oxygen. Geolite is an example of a medium with
excellent aeration. In some hydroponic systems, a nutrient solution is aerated by
the output of an aquarium pump.

AEROPONICS
A system in which the roots of a plant are consistently or intermittently misted
with fine droplets of nutrient solution.

ACID
Refers to medium or nutrient solution with a low pH; an acidic solution has a pH
below 7.

ALKALINE
Refers to medium or nutrient solution with a high pH; any pH over 7 is considered
alkaline.

BORON (B)
The function of this micronutrient is not well understood, but it is suspected that
it might aid carbohydrate transport.

BURN
Leaf tips that turn dark from excess fertilizer and salt burn.

CALCIUM (Ca)
Calcium is vital in all parts of plants to promote the translocation of carbohydrates,
healthy cell wall structure, strong stems, membrane maintenance and root structure
development. Calcium is a macronutrient.

CARBON DIOXIDE (CO2)
A colorless, odorless, tasteless gas in the air necessary for plant life. Occurs
naturally in the atmosphere at .03%.

CHLORINE (Cl)
This micronutrient is essential for photosynthesis, where it acts as an enzyme activator
during the production of oxygen from water.

CHLOROSIS
The condition of a sick plant with yellowing leaves due to inadequate formation
of chlorophyll. Chlorosis is caused by a nutrient deficiency, usually iron or nitrogen;
nutrient deficiencies are themselves often caused by a pH that is out of the acceptable
range.

CLONE
A plant produced through asexual reproduction including, but not limited to, cuttings,
layering and tissue culture.

CONDITIONING
To soak new Rockwool in an acidic solution to lower the pH from 8.0 to 5.5.

COPPER (Cu)
This micronutrient is an internal catalyst and acts as an electron carrier; it is
also believed to play a role in nitrogen fixation.

DAMPING-OFF FUNGUS
Disease that attacks young seedlings and cuttings, causing stems to rot at the base;
overwatering is the main cause of damping-off.

DISSOLVED SOLIDS or TOTAL DISSOLVED SOLIDS
The amount of dissolved solids, usually fertilizer salts, that are measured in water
in parts per million.

DRIP AERATION
A hydroponic method wherein air pressure from a small air pump is used to percolate
nutrient solution out through a ring of feeder tubing which encircles the plant.

DRIP SYSTEM (DRIP EMITTER SYSTEM)
A very efficient watering system that employs a main hose with small water emitters.
Water is metered out of the emitters, one drop at a time.

EBB-AND-FLOW (or FLOOD and DRAIN)
A hydroponic system in which the medium, usually aggregate pebbles, is periodically
flooded with nutrient solution and then drained again, feeding and aerating the
medium and root system.

FOLIAR FEEDING
Misting plants with fertilizer solution, which is absorbed by the foliage.

FUNGICIDE
A product that destroys or inhibits fungus.

FUNGUS
Any of a major group (Fungi) of saprophytic and parasitic spore-producing organisms
usually classified as plants that lack chlorophyll and include molds, rusts, mildews,
smuts, mushrooms, and yeasts. Common fungal diseases that attack plants are "damping-off,"
Botrytis, and powdery mildew.

GERMINATION
The process of causing the initiation and development of a plant from seed.

GEOLITE
One of several brand names/varieties of clay aggregate medium (also known as LECA
for light expanded clay aggregate). It is a lightweight, porous substrate with excellent
aeration. Because it does not really wick water effectively, Geolite and other LECA
mediums are favorites in ebb-and-flow and drip hydroponic systems.

HARDEN-OFF
To gradually acclimatize a plant to a more harsh environment. A seedling must be
hardened-off before planting outdoors.

HORMONE
Chemical substance that controls the growth and development of a plant. Root-inducing
hormones help cuttings root.

HYBRID
The offspring from two plants of different breeds, variety or genetic make-up.

HYDRATED LIME
Instantly soluble lime, used to raise or lower pH.

HYGROMETER
An instrument for measuring relative humidity in the atmosphere.

IRON (Fe)
This micronutrient acts as a catalyst in the photosynthesis/respiration process,
and is essential for the formation of sugars and starches. Iron also activates certain
other enzymes.

LEAF CURL
Leaf malformation due to overwatering, over fertilization, lack of magnesium, insect
or fungus damage or negative tropism.

MACRONUTRIENTS
The primary nutrients N-P-K or the secondary nutrients magnesium and calcium.

MANGANESE (Mn)
This micronutrient activates one or more enzymes in fatty acid synthesis; it also
activates the enzymes responsible for DNA and RNA production. Closely associated
with copper and zinc, manganese also participates directly in the photosynthetic
creation of oxygen from water.

MEDIUM
The substrate or soilless material which supports the plant and absorbs and releases
the nutrient solution in hydroponic horticulture.

MICRONUTRIENTS
Also referred to a TRACE ELEMENTS, including S, Fe, Mn, B, Mb, An and Cu.

MOLYBDENUM (Mo)
This micronutrient is essential for nitrogen fixation and nitrate reduction.

NECROSIS
The dying of plant tissue, usually the result of serious nutrient deficiency or
pest attack.

NITROGEN (N)
Nitrogen is used in various forms to promote rapid vegetative growth, leaf, flower,
fruit and seed development, and chlorophyll development; and to increase the protein
content in all plants.

NFT (NUTRIENT FILM TECHNIQUE)
A hydroponic method in which nutrient is fed into grow tubes or trays in a thin
film where the roots draw it up. This "nutrient film" allows the roots to have constant
contact with the nutrient and the air layer above at the same time.

NUTRIENTS
The elements needed by plants for normal growth and health. The major nutrients
(MACRONUTRIENTS) are nitrogen (N), phosphorus (P), and potassium (K), but there
are numerous MICRONUTRIENTS (also called TRACE ELEMENTS) which also have integral
roles in maintaining plant health. A good quality hydroponic nutrient formula will
contain all of the major nutrients and micronutrients needed by the vast majority
of plants.

NUTRIENT SOLUTION
The mixture of water and water-soluble nutrients which is provided to the plants
for nourishment in a hydroponic system.

NUTRIENTS, SECONDARY
The elements other than N, P and K which are considered nearly as important as N,
P and K but are not considered micronutrients. Calcium (Ca), magnesium (Mg), and
sulphur (S) are the elements usually referred to by this term.

pH
A scale from 1 to 14 that measures the acid to alkaline balance of a growing medium
(or any other substance). In general, plants grow best in a pH range of 6 to 6.8;
6.3 is considered ideal. If the pH is not within the acceptable range, nutrients
may not be absorbed to maximum capacity.

PHOSPHORUS (P)
Phosphorus promotes and stimulates early growth and blooming and root growth. It
hastens maturity and seed growth, and contributes to the general hardiness of plants.
Phosphorus is a macronutrient.

POTASSIUM (K)
Potassium promotes disease resistance and good development of carbohydrates, starches
and sugars, and it increases fruit production. Potassium is a macronutrient.

PERLITE
1. Sand or volcanic glass which has been expanded by heat; perlite holds water and
nutrients on its many irregular surfaces.
2. Mineral soil amendment.

PHOTOPERIOD
Day length; the relationship between the length of light and dark in a 24 hour period.

PHOTOSYNTHESIS
The process by which plants use light energy to collect carbon dioxide from the
atmosphere and convert it to chemical energy in the form of sugar.

PROPAGATE
Sexual propagation: to produce seed by breeding different male and female flowers.

Asexual propagation: to produce plantlets (also known as CLONES) by taking cuttings.

PYRETHRUM
Natural insecticide made from the blossoms of various chrysanthemums.

RESERVOIR
The container in a hydroponic system which holds nutrient solution in reserve for
use.

ROCKWOOL
Inert, soilless growing medium consisting of woven, thin strand-like fibers made
from molten volcanic rock and limestone, which is heated to over 2900 degrees F,
extruded, and formed into slabs, cubes and blocks.

SECONDARY NUTRIENTS
Calcium (Ca) and magnesium (Mg) are considered to be the secondary nutrients.

SYSTEMIC
Used in reference to a disease within the plant tissue, not initiated from the external
cells. Also refers to materials and compounds which are taken up or absorbed by
the plant and designed to fight disease (e.g. systemic fungicide).

VERMICULITE
Mica which has been processed and expanded by heat. Vermiculite has excellent water-retention
qualities and is a good soil amendment and medium for rooting cuttings.

WICK
Part of a passive hydroponic system using a wick suspended in the nutrient solution.
The nutrients pass up the wick and are absorbed by the medium and roots.

ZINC (Zn)
Like copper and manganese, zinc is linked to chlorophyll synthesis.